1. Field of the Invention
The present invention relates to an electromagnetic actuating system of an internal combustion engine, and particularly to an electromagnetic actuating system of an internal combustion engine which actuates an intake valve or an exhaust valve by cooperation of an electromagnetic force generated by an electromagnet and a resilient force generated by a spring.
2. Description of the Related Art
Conventionally, as disclosed in Japanese Laid-Open Patent Application No. 59-213913, there is known a solenoid valve having an engine valve which functions as an intake valve or an exhaust valve of an internal combustion engine. An armature is connected to the engine valve. Hereinafter, the engine valve and the armature are referred to as a movable part.
An upper electromagnet and an upper spring are disposed above the armature, and a lower electromagnet and a lower spring are disposed below the armature. The armature is held at a neutral position between the upper and lower electromagnets by the upper and lower springs. Each of the upper and lower electromagnets generates an electromagnet force which attracts the armature by being supplied with an exciting current.
According to the above-mentioned conventional solenoid valve, the movable part can be moved toward the upper electromagnet by supplying an exciting current to the upper electromagnet. Similarly, the movable part can be moved toward the lower electromagnet by supplying an exciting current to the lower electromagnet. Thus, according to the conventional solenoid valve, it is possible to actuate the intake valve or the exhaust valve to be closed and opened by alternately supplying exciting currents to the upper and lower electromagnets at appropriate timings.
In the conventional solenoid valve, when the movable part is in a fully closed position or a fully opened position, the movable part can promptly start being actuated in response to a request by cooperation of the electromagnetic force generated by the upper or lower electromagnet and a resilient force generated by the upper or lower spring. On the other hand, when power supply to the solenoid valve is shut off, the movable part is held at a neutral position between the fully closed position and the fully opened position since neither the upper electromagnet nor the lower electromagnet is energized. In this state, the armature is spaced away from both the upper and lower electromagnets and resilient forces of the upper and lower springs exerted on the armature are balanced. Thus, in order to start actuating the movable part from the neutral position, it is necessary to exert an electromagnetic attracting force on the armature spaced away from the electromagnets in a situation where the resilient forces of the springs cannot be used. Therefore, when the movable part is at the neutral position, electric power to be supplied to the electromagnet becomes large, and, additionally, it is difficult to promptly operate the solenoid valve.
For this reason, in the above-mentioned conventional solenoid valve, exciting currents are alternately supplied to the upper and lower electromagnets with a period corresponding to a natural vibration period of the movable part when the internal combustion engine is started. According to this technique, the movable part can be moved from the neutral position to the fully closed position or the fully opened position by a resonance phenomenon of the movable part. Hereinafter, the above-mentioned process of, when the engine is started, moving the movable part to the fully closed or opened position by exciting a natural vibration of the movable part is referred to as an initial actuation.
However, when the initial actuation is performed, a large operating sound is generated by a vibration of the movable part. Additionally, since exciting currents must be alternately supplied to the upper and lower electromagnets, power consumption of the solenoid valve becomes large.
In view of these disadvantages of the initial actuation, Japanese Laid-Open Patent Application No. 10-138110 discloses a solenoid valve which can maintain the movable part in the fully closed position without performing the initial actuation. This solenoid valve includes a solenoid which is provided to the upper spring at one end thereof opposite to the armature. When the solenoid is not energized, the upper spring is upwardly retracted. In this state, the armature is in contact with the upper electromagnet. On the other hand, when the solenoid is energized, the upper spring is downwardly pressed toward the armature by the solenoid. In this state, the armature is held in the neutral position. Thus, according to the above-mentioned structure, it is possible to hold the movable part in the fully closed position by simply de-energizing the solenoid.
However, when the engine is operating, the movable part must be actuated by the upper and lower electromagnets with the neutral position being a center of movement of the movable part. Thus, when the engine is operating, it is necessary to energize the solenoid so as to maintain a state where the upper spring is pressed toward the armature, resulting in increased power consumption of the solenoid valve.